Infection with HCV is a major cause of human liver disease throughout the world. Chronic infection with HCV is associated with chronic liver disease, cirrhosis, hepatocellular carcinoma, and liver failure. HCV is a hepacivirus member of the Flaviviridae family of RNA viruses that affect animals and humans. The genome is a single ˜9.6-kilobase strand of RNA, and consists of one open reading frame that encodes for a polyprotein of ˜3000 amino acids flanked by untranslated regions at both 5′ and 3′ ends (5′- and 3′-UTR). The polyprotein serves as the precursor to at least 10 separate viral proteins critical for replication and assembly of progeny viral particles. The organization of structural and non-structural proteins in the HCV polyprotein is as follows: C-E1-E2-p7-NS2-NS3-NS4a-NS4b-NS5a-NS5b. While the pathology of HCV infection affects mainly the liver, the virus is found in other cell types in the body including peripheral blood lymphocytes.
HCV is a major causative agent for post-transfusion and for sporadic hepatitis. Infection by HCV is insidious in a high proportion of chronically infected, and infectious, carriers who may not experience clinical symptoms for many years. An estimated 170 million chronic carriers worldwide are at risk of developing liver disease.
Due to the high degree of variability in the viral surface antigens, existence of multiple viral genotypes, and demonstrated specificity of immunity, the development of a successful vaccine in the near future is unlikely. Alpha-interferon, alone or in combination with ribavirin, has been widely used for treatment of chronic HCV infection. However, treatment of HCV with interferon has frequently been associated with adverse side effects such as fatigue, fever, chills, headache, leukopenia, thrombocytopenia, psychiatric effects and associated disorders, autoimmune phenomena and associated disorder and thyroid dysfunction. Ribavirin, an inhibitor of inosine 5′-monophosphate dehydrogenase (IMPDH), enhances the efficacy of IFN-alpha in the treatment of HCV. Despite the introduction of ribavirin, more than 50% of the patients do not eliminate the virus with the current therapy of interferon-alpha (IFN) and ribavirin. With the introduction of pegylated interferon, both initial and sustained response rates have improved, and combination treatment of Peg-IFN with ribavirin until recently, constituted a standard for therapy. However, the side effects associated with combination therapy persist. Ribavirin causes significant hemolysis in 10-20% of patients treated at currently recommended doses, and the drug is both teratogenic and embryotoxic.
Most recently, oral agents including Sofosbuvir were introduced as a component of a combination antiviral regimen for patients with HCV mono-infection and HCV/HIV-1 coinfection. Treatment regimen and duration are dependent on both viral genotype and patient population and can vary from 8 to 24 weeks. Consequently, a prescribed treatment requires ingestion of a daily regimen which can lead to reduced patient compliance resulting in reduced drug efficacy and development of resistant strains of HCV. In highly motivated populations, adherence to these shorter duration therapies can be good and cure rates can be very high. In marginal populations such as IV drug abusers, the homeless, and the mentally ill, adherence to regimens may be poorer and a lack of adherence may result in treatment failure and development of long-lived resistance mutations in the HCV genome. Additionally for some populations, such as incarcerated patients, the associated cost of each treatment (dose) may be very high.
Accordingly, successful long acting treatments for HCV infected patients which reduce the number of treatments down to even a single treatment can alleviate compliance issues and issues associated with the cost of treatment This would represent a significant advance for HCV patients.